Melting crucible and cooling means therefor



Feb.'26, 1963 D. E. COOPER ET AL MELTING CRUCIBLE AND COOLING MEANS THEREFOR Filed April 24, 1959 INVENTORS Donald E. Cooper Elmer D. Dilling United States PatentOfilice 3,078,529 Patented Feb. 26, 1963 3,078,529 MELTBNG CRUCIBLE AND COULING MEANS THEREFOR Donald E. Cooper and Elmer D. Dilling, Las Vegas, Nev., assignors to Titanium Metals Corporation of America, New York, N.Y., a corporation of Delaware Filed Apr. 24, 1959, Ser. No. 808,811 2 Claims. (Cl. 22-144) This invention relates to a melting crucible, and more particularly to a crucible and cooling means therefore for use in arc melting metals. Such crucibles are often referred to as of the cold mold type.

In cold mold arc melting furnaces, the crucible, or mold, itself is generally fabricated as a thin wall copper vessel surrounded by a jacket through which water is circulated as a cooling fluid. An arc is maintained between metal in the crucible and an electrode, which may be consumable or non-consumable, and a solid ingotis for-med in the crucible by progressive solidification of molten transferred metal. Such apparatus is inherently dangerous because perforation of the crucible wall by the are results in inflow of water onto hot and molten metal.

A disastrous explosion can occur under such conditions.

In addition, Water cooled crucibles are diflicult to maintain at wall temperatures much above 100 C., the boiling point of water.

It is therefore a principal object of this invention to provide an improved crucible and cooling means therefor for use in arc melting furnaces of the cold mold type. Another object of this invention is to provide a safe crucible for use in arc melting furnaces of the cold mold type. A still further object of this invention is to provide an improved crucible, for an arc melting furnace of the cold mold type, having improved means for cooling and temperature control. These and other objects of this invention will be apparent from the following detailed description thereof and from the annexed drawings in which:

FIG. 1 illustrates a general view of apparatus embodying features of this invention with the crucible shown in a vertical sectional view.

FIG. 2 illustrates a sectional view of the apparatus of FIG. 1 taken along the line 22.

Referring to FIGS. 1 and 2, a crucible indicated generally at It comprises an inner shell 12 having upper outwardly extending flange 14 and lower outwardly extending flange 16. Attached to one of these flanges, for example, the lower flange 16, as shown, is one end of outer shell 18 which is spaced apart from inner shell 12, defining cooling jacket 20. The top or other end, of shell 1-8 is not attached to upper flange 14- but is spaced apart therefrom as shown. Depending from flange 14 and spaced apart from and overlapping the top of outer shell 18, is collar 22 which isfixedly attached as by welding to the outer edge of flexible, transversely a-rcuate ring 24, whose inner edge is likewise fixedly attached as by welding to shell 18 at a position spaced apart from its upper extremity.

The lower end of crucible is closed by provision of preferably detachable bottom 26 in which is provided a cooling duct or jacket 28 in the area adjacent the interior of shell 12. Bottom 26 is attached to lower flange 16 of inner shell 12 by provision of a slot pin and slot hinge comprising horizontal pin 30, attached to arm 32, and which engages vertical slots 34 in spaced apart brackets 36 which extend from flange 16. Means for sealing the bottom 26 to flange 16 are provided which comprise gasket 38 interposed therebetween and maintained in position by groove 40 in flange 16. Slots 34 provide for vertical motion of bottom so that when it is in closed position it may be firmly tightened in place as by bolts 42.

Mean-s are provided for circulating liquid metal in jackets 2t) and 28, with such metal being transferred through these jackets and through a heat exchanger external of the crucible 10. Liquid metal from jackets 20 and 28 is transferred by electromagnetic pump 44-, which is of conventional design and construction and is not here described in detail, through pipe 46 which leads through collar 22 as at 48. From the space between collar 22 and the upper end of outer shell 18, liquid metal flows over the top of shell 18 and around and down jacket 20 being withdrawn through nipple 50. Flexible pipe 52 connects nipple Sit to nipple 54 which leads the liquid metal into jacket 28 from which it flows out through nipple 56 into flexible pipe 58. Pipe 60 connects pipe 58 to heat exchanger 62 in which heat in the liquid metal is abstracted conveniently by air forced by fan 64 passing over tubes 66. Pipe 68 connects the heat exchanger to the intake of electromagnetic pump 44 which re-circulates the cooled liquid metal back through the system. While the liquid metal flow has been described above for purposes of illustration, it will be apparent that the direction of liquid metal flow through the system may be the reverse of that described with the same effects and advantages obtained.

Means are provided for attaching crucible 10/ to apparatus for positioning and driving an electrode '70 and which apparatus will be wholly or in part enclosed, the lower part of such enclosure represented in FIG. 1 by shell '72 to which is attached extending flange 74. A suitable gasket 76 is interposed between flanges 74 and 14 which are firmly tightened together by bolts 78 provided with insulating sleeves 80. Connection of one lead from a power source to inner shell 12 may conveniently be accomplished by terminal 82 which is tightened in electrical contact with flange 14 by one of bolts 78. The electrode positioning and driving apparatus itself forms no part of this invention and is referred to herein only for ready understanding of the attachment of the crucible assembly thereto.

The inner shell 12 may advantageously be of copper to provide good heat transfer from its inner surface to the liquid metal in jacket 29. The outer shell 18 is advantageously fabricated of steel. Due to temperature differential, and different construction materials if employed, the thermal expansion of inner shell 12 will be different from that of outer shell 18. It is a unique feature and an important advantage of the organization described that differential expansion of these elements can occur without straining the construction which could result in serious leaks of liquid metal. It is important that the top of outer shell 18 be spaced apart from the under surface of flange 14 a distance greater than its longitudinal expansion in operation, thus providing clearance "for such expansion and also providin a restricted passageway for liquid metal entering jacket 20. The liquid metal flowing through jacket 24 is thereby forced to flow close to the juncture of flange l4- and the top of inner shell 12 to adequately cool this ordinarily critical area. Ring 24 is preferably fabricated of relatively thin or flexible metal and its transversely arcuate design has the important effect of provid ing ready flexure across its width without strain on the weldments by which it is attached to collar 22 and shell 18.

The liquid metal useful as a heat exchange medium is preferably an alloy of sodium and potassium but may also be lead, bismuth or other metal or alloy which is liquid at the temperature of operation. An alloy of 54% sodium and 44% potassium is particularly advantageous having a melting point of about 19 C. Sodium and potassium particularly should not be exposed to air, and ignite readily if leaks permit escape of metal to the atmosphere. Therefore the crucible of this invention provides for melting and discharge of an ingot without disconnecting or breaking any cooling metal lines or joints.

In operation, the crucible assembly of this invention is 3 employed as part of arc melting apparatus which will include mechanism for driving or positioning an electrode. The electrode may be consumable or non-consumable. Such mechanisms are well known in the art and will not herein be described in detail. Since the melting operation will be carried out in an atmosphere of inert or other special gas, or under vacuum, the electrode driving mechanism will be enclosed, at least in part, in a suitable housing, the bottom portion thereof, as previously described, shown as shell 72 and flange '74. The crucible it? is attached to the driving mechanism and other auxiliary appa ratus by placing flanges 74- and 14 in juxtaposition with gasket 76 interposed therebetween, and bolts 78 are placed and tightened to provide a gas tight seal at the juncture of these furnace elements. The bottom 26 is set in closed position and sealed by tightening bolts 42.

The melting operation is then conducted according to known methods. If the electrode '70 is consumable, the metal of which it is composed will be melted and transferred to form an ingot in the crucible 10, the melting are being maintained by electric power connected by suitable means (not shown) to electrode 78 and to the crucible and metal therein through terminal 82 and flange 14 to inner crucible wall 12. If the electrode is non-consumable, suitable feed means will be provided to supply metal to be melted to the arc zone, and a similar ingot obtained in the crucible.

During melting the crucible is cooled by circulation of liquid metal through the jacket 20 formed by inner shell 12 and outer shell 18 and through the jacket 28 in the crucible bottom. The liquid metal, preferably an alloy of sodium and potassium, is circulated by electromagnetic pump 44 through the crucible and also through heat exchanger 62 so that its temperature at the supply point to the crucible is as cool as desired. It will be appreciated that the speed of circulation of the liquid metal and the amount of heat abstracted therefrom by the heat exchanger may be adjusted to maintain the proper crucible operating temperature, which may if desired be substantially higher than that normally maintained by water circulation, but will be below any critical temperature imposed by material employed in the fabrication of the crucible.

After melting is complete the ingot is preferably cooled somewhat in place by simply continuing to circulate cooling liquid metal, and then the bolts 42 are loosened and the bottom 26 of the crucible is detached and swung down on its hinge, and the ingot removed preferably downwardly from crucible inner shell 12. After necessary cleaning of the interior of crucible shell 12 the bottom 26 is swung up in place again and bolts 42 securely tightened and the crucible is ready for another cycle of melting operation.

Employment of a liquid metal cooling medium, instead of Water heretofore employed in crucibles for are melting, provides a much safer apparatus. Occasionally the arc in the crucible will Wander to, and perforate, the crucible inner shell. If this occurs, when water is used as a cooling medium, entry of water into the crucible proper and contact with molten metal therein can result in disastrous explosion. liquid metal is employed as a cooling medium as described herein. In addition, better temperature control can be The explosion hazard is eliminated when,

maintained at high or low temperatures, than with Water, whose boiling point of C. limits its useful applications.

We claim:

1. In a crucible for use in are melting apparatus and in which a liquid metal is employed as a fluid coolant, the improvements which comprise; and inner shell having an outwardly extending top flange and an outwardly extending bottom flange, an outer shell surrounding said inner shell and having one of its ends fixedly attached to one of said flanges, the other end of said outer shell being spaced apart from the other of said flanges by a distance greater than the longitudinal thermal expansion of said outer shell in operation to provide a passageway therebetween, a collar fixedly attached to said other flange and surrounding and overlapping the said other end of said outer shell and spaced apart therefrom, a transversely arcuate flexible metallic ring fixedly attached to said collar and to said outer shell and means for circulating a liquid metal coolant through the space between said inner and outer shells, through the passageway between the said other end of said outer shell and the said other flange and through the space between said collar and said outer shell.

2. In a crucible for use in arc melting apparatus and in which a liquid metal is employed as a fluid coolant, the improvements which comprise; an inner shell having an outwardly extending top flange and an outwardly extending bottom flange, an outer shell surrounding said inner shell and having one of its ends fixedly attached to one or" said flanges, the other end of said outer shell being spaced apart from the other of said flanges by a distance greater than the longitudinal thermal expansion of said outer shell in operation to provide a restricted passageway therebetween, a collar fixedly attached to said other flange and surrounding and overlapping the said other end of said outer shell and spaced apart therefrom, a transversely arcuate flexible metallic ring fixedly attached to said collar and to said outer shell and means for circulating a liquid metal coolant through the space between said inner and outer shells, through the restricted passageway between the said other end of said outer shell and the said other flange and through the space between said collar and said outer shell.

References Cited in the file of this patent UNITED STATES PATENTS 1,112,937 Rowley Oct. 6, 1914 1,936,280 Williams Nov. 21, 1933 1,988,425 Summey Jan. 15, 1935 2,357,780 Muller Sept. 5, 1944 2,392,267 Salliover Jan. 1, 1946 2,665,318 Herres Jan. 5, 1954 2,761,002 Laird et al Aug. 28, 1956 2,762,097 Kruger Sept. 11, 1956 2,828,201 Findlay Mar. 25, 1958 2,862,265 Vaughn et al Dec. 2, 1958 2,883,721 Gorga et al. Apr. 28, 1959' 2,885,751 Hornak et al May 12, 1959 2,887,722 Bauers May 26, 1959 FOREIGN PATENTS 503,201 Great Britain Mar. 31, 1939 

1. IN A CRUCIBLE FOR USE IN ARC MELTING APPARATUS AND IN WHICH A LIQUID METAL IS EMPLOYED AS A FLUID COOLANT, THE IMPROVEMENTS WHICH COMPRISE; AND INNER SHELL HAVING AN OUTWARDLY EXTENDING TOP FLANGE AND AN OUTWARDLY EXTENDING BOTTOM FLANGE, AN OUTER SHELL SURROUNDING SAID INNER SHELL AND HAVING ONE OF ITS ENDS FIXEDLY ATTACHED TO ONE OF SAID FLANGES, THE OTHER END OF SAID OUTER SHELL BEING SPACED APART FROM THE OTHER OF SAID FLANGES BY A DISTANCE GREATER THAN THE LONGITUDINAL THERMAL EXPANSION OF SAID OUTER SHELL IN OPERATION TO PROVIDE A PASSAGEWAY THEREBETWEEN, A COLLAR FIXEDLY ATTACHED TO SAID OTHER FLANGE AND SURROUNDING AND OVERLAPPING THE SAID OTHER END OF SAID OUTER SHELL AND SPACED APART THEREFROM, A TRANSVERSLY 